1. Field of the Invention
The present invention relates to a high-pressure fuel injection pipe having a small outer diameter in the range from 4.5 to 20.0 mm and a large wall thickness in the range from 1.5 to 8.0 mm and a method of manufacturing the same and, more particularly, to a method of manufacturing a high-pressure fuel injection pipe used in a diesel internal combustion engine.
In the present specification, the term xe2x80x9chigh-pressure fuel injection pipexe2x80x9d is a general term which implies not only pipe materials for high-pressure injection pipes before formation of a head portion at a connecting end thereof but also materials which have been formed with such a head portion and materials which have been bent after the formation of a head portion and, further, so-called common rails serving as a pressure accumulation chamber for accumulating the pressure of fuel which has been pressurized in advance using a high-pressure pump and for supplying the fuel to a combustion chamber via a mechanically or electrically controlled valve.
2. Description of the Prior Art
Recently, there is an accelerating trend toward an increase in the pressure of fuel to be supplied to a high pressure fuel injection pipe used as a fuel injection pipe for a diesel engine as a measure for reducing NOx and black smoke, and this has resulted in a need for fuel injection for an injection period of 1 to 2 msec., at a maximum flow rate of 50 m/sec. and at a high internal pressure in the range from 60 to 1500 bar (peak value).
Such a change in market demands is accompanied by an increased possibility of clogging of an injection nozzle caused by foreign particles such as metal particles which have stuck to the inner surface of a high-pressure fuel injection pipe after floating in the air or entering from the outside, and this can cause a faulty operation of a diesel engine or damage to a fuel pump. Thus, it is an important problem to be solved to improve the cleanness of the inner surface of a high-pressure fuel injection pipe in order to prevent this.
In conventional steps of manufacturing a high-pressure fuel injection pipe, foreign particles that enter such an injection pipe and stick to the inner circumferential surface thereof have been cleaned by simply blowing them off with high-pressure air. However, this has not provided for sufficient cleaning and still has left a possibility of clogging of an injection nozzle which leads to a faulty operation of a diesel engine and damage to a fuel injection pump. Under such circumstances, there is a need for further improvement.
The present invention has been conceived in consideration to the above-described situation of this type of high-pressure fuel injection pipe, and it is an object of the present invention to provide a method of manufacturing a high-pressure fuel injection pipe in which the cleanness of the inner surface of a high-pressure fuel injection pipe can be improved by substantially completely eliminating various foreign particles from the inner circumferential surface thereof to prevent the occurrence of clogging of an injection nozzle and to thereby prevent a faulty operation of a diesel engine and damage to a fuel pump.
In order to achieve the above-described object, according to the present invention, there is provided a method of manufacturing a high-pressure fuel injection pipe characterized in that steps of manufacturing a metal pipe having a large wall thickness and a small diameter include cleaning utilizing a solvent for dissolving foreign particles that follows a final pipe-extending step. The above-mentioned solvent for dissolving foreign particles is preferably an acid, alkaline or organic solvent, and such cleaning utilizing the solvent for dissolving foreign particles is preferably repeated a plurality of times utilizing different kinds of solvents or the same kind of solvent.